[PATCH] D73210: [OPT_DPG][LIVEDEBUGVALUES] Teach Live Debug Values About Meta Instructions

[Tom Weaver via Phabricator via llvm-commits]

TWeaver created this revision.
TWeaver added reviewers: vsk, dstenb, dblaikie, aprantl, djokov.
TWeaver added a project: debug-info.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

Previously LiveDebugValues pass would consider meta instructions that 'fiddle' with liveness of registers as register definitions when transfering register defs. This would mean that, for example, a KILL instruction would cause LiveDebugValues to terminate the range of an earlier DBG_VALUE instruction resulting in the none propogation of said DBG_VALUE instructions into later blocks.

This patch adds the check and a helpful comment, fixes a test that previously tested for the broken behaviour by coincidence and adds a test specifically for this.

Thanks for your time reviewing!


https://reviews.llvm.org/D73210

Files:
  llvm/lib/CodeGen/LiveDebugValues.cpp
  llvm/test/DebugInfo/MIR/X86/entry-value-of-modified-param.mir
  llvm/test/DebugInfo/MIR/X86/livedebugvalues-ignores-metaInstructions.mir


Index: llvm/test/DebugInfo/MIR/X86/livedebugvalues-ignores-metaInstructions.mir
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/MIR/X86/livedebugvalues-ignores-metaInstructions.mir
@@ -0,0 +1,64 @@
+--- |
+  ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
+
+  ; Check that live-debug-values ignores meta instructions.
+
+  ; CHECK-LABEL: bb.0.entry:
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK-LABEL: bb.1.bb1:
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK-LABEL: bb.2.bb2:
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK-LABEL: bb.3.bb3:
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+
+  define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
+  entry:
+    br label %bb1, !dbg !17
+  bb1:
+    br label %bb2, !dbg !17
+  bb2:
+    br label %bb3, !dbg !17
+  bb3:
+    ret i32 0, !dbg !17
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!7, !8, !9, !10}
+  !llvm.ident = !{!11}
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, debugInfoForProfiling: true, nameTableKind: None)
+  !1 = !DIFile(filename: "main.cpp", directory: "F:\")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
+  !5 = distinct !DIGlobalVariable(name: "start", scope: !0, file: !1, line: 4, type: !6, isLocal: false, isDefinition: true)
+  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !7 = !{i32 2, !"Dwarf Version", i32 4}
+  !8 = !{i32 2, !"Debug Info Version", i32 3}
+  !9 = !{i32 1, !"wchar_size", i32 2}
+  !10 = !{i32 7, !"PIC Level", i32 2}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "bb_to_bb", linkageName: "bb_to_bb", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!6, !6}
+  !15 = !{!16}
+  !16 = !DILocalVariable(name: "myVar", scope: !12, file: !1, line: 7, type: !6)
+  !17 = !DILocation(line: 10, scope: !12)
+
+...
+---
+name:            _Z8bb_to_bb
+body:             |
+  bb.0.entry:
+    successors: %bb.1
+    $ebx = MOV32ri 0, debug-location !17
+    DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  bb.1.bb1:
+    successors: %bb.2
+    renamable $ebx = KILL $ebx
+  bb.2.bb2:
+    successors: %bb.3
+    renamable $ebx = KILL $ebx
+  bb.3.bb3:
+    RETQ $eax, debug-location !17
+...
Index: llvm/test/DebugInfo/MIR/X86/entry-value-of-modified-param.mir
===================================================================
--- llvm/test/DebugInfo/MIR/X86/entry-value-of-modified-param.mir
+++ llvm/test/DebugInfo/MIR/X86/entry-value-of-modified-param.mir
@@ -103,7 +103,7 @@
     CFI_INSTRUCTION offset $rbx, -16
     $ebx = MOV32rr $esi
     DBG_VALUE $ebx, $noreg, !17, !DIExpression(), debug-location !20
-    renamable $edi = KILL $edi, implicit-def $rdi
+    $edi = MOV32ri 5, debug-location !22
     DBG_VALUE $edi, $noreg, !16, !DIExpression(), debug-location !20
     renamable $edx = LEA64_32r killed renamable $rdi, 1, $noreg, 2, $noreg, debug-location !21
     DBG_VALUE $edx, $noreg, !19, !DIExpression(), debug-location !20
Index: llvm/lib/CodeGen/LiveDebugValues.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugValues.cpp
+++ llvm/lib/CodeGen/LiveDebugValues.cpp
@@ -922,6 +922,12 @@
 void LiveDebugValues::transferRegisterDef(
     MachineInstr &MI, OpenRangesSet &OpenRanges, VarLocMap &VarLocIDs,
     TransferMap &Transfers) {
+
+  // Meta Instructions do not affect the debug liveness of any register they
+  // define.
+  if (MI.isMetaInstruction())
+    return;
+
   MachineFunction *MF = MI.getMF();
   const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
   unsigned SP = TLI->getStackPointerRegisterToSaveRestore();


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